If this is the Eric that had the 4-6-0 at Norm O scale, I have a thought. Did that wire go to the head light, and maybe it became detached before or during disassembling. Therefore the frame and engine body would along with the motor and light would be one pole and the other wire would go to the tender to complete the circuit. I believe I have the same steam engine. I would be willing to let take a look. Hope this helps.